I have a 3D tube that is curved.
The tube is turned in a rather peculiar position.

For my drawing, I'd like to represent the tube as if it were lying flat on a table (there has to be a position where the lower generatrix of the tube is in contact with the table at every point).

So I'm trying to create the plane tangeant to the green face of the tube, so that I can then have something physical to hold